1. Field of the Invention
The present invention relates generally to a data format for data being recorded on a recording medium, a data recording/reproducing apparatus, and a data recording/reproducing method. The present invention particularly relates to a data format for realizing effective error correction for errors that occur due to dust and/or scratches, for example, on the recording medium.
2. Description of the Related Art
Various types of data recording/reproducing apparatuses exist including those for recording data on a recording medium such as a magnetic disk, a magnetic tape, an optical disk, and a magneto-optical disk. To record data on these recording media, a magnetic recording mark is usually used. These recording media are less expensive than semiconductor memory and are able to store data on a permanent basis. Also, these recording media are widely used as information recording media for computers to handle large amounts of information such as images and image information. It is desired that a recording/reproducing apparatus for recording data on such recording media be able to operate with high reliability and effectively correct data errors occurring as a result of dust and scratches on the recording media.
FIG. 1 is a diagram illustrating ECC (error correcting code) sectors, their respective data formats, and a corresponding recording data sequence according to a conventional scheme. As is shown in part (A) of FIG. 1, the recording data includes plural ECC sectors, ECC sector 0 (100), ECC sector 1 (110), ECC sector 2n−1 (120), and ECC sector 2n (130). As is shown in part (B) of FIG. 1, each ECC sector is further divided into plural data blocks. For example, the ECC sector 0 (100) includes data 0/0 (101), data 0/1 (102), and data 0/15 (103) as data blocks. Each data block includes header information that indicates the head of the data block and data contents.
A data recording/reproducing apparatus uses an error correcting code (ECC) to accurately restore data recorded on a recording medium. When the data recording/reproducing apparatus reproduces data of a recording medium, the data reproduced from the recording medium may be erred or parts of the data may be skipped due to influence of dust and scratches, for example, on the recording medium. Accordingly, redundancy data are added to the original recording data so that data may be accurately reproduced from the recording medium even when such data error occurs, and the redundancy data are used to correct errors and inadequacies upon relaying the data.
As the ECC format, the parity code and the CRC code are known. Also, the Reed-Solomon code is known as a representative format for the ECC. Any of these ECC formats may be used to encode data recorded on a recording medium to generate an ECC sector therefrom. In other words, an ECC sector corresponds to a group of data that are encoded by an error correcting code. Further, an ECC sector such as the ECC sector ECC 0 (100) of FIG. 1 may be divided into data blocks such as data 0/0 (101), data 0/1 (102), and data 0/15 (103), for example. Each data block may be arranged to include a header at its front end portion for enabling detection of the head of the data block upon reproducing the data block.
The data blocks divided in the above-described manner may then be recorded on a recording medium. The recording data sequence shown in part (C) of FIG. 1 indicates the order in which the divided data blocks of the ECC sectors are to be recorded. As is shown in this drawing, the data sequence is recorded according to the order in which the divided data blocks are arranged.
In the following, the data recording/reproducing apparatus that conducts such an operation is described. FIG. 2 is a block diagram showing an exemplary configuration of a data recording/reproducing apparatus. The data recording/reproducing apparatus 200 of FIG. 2 includes an ECC encoder 201, a modulator 202, a recording circuit 203, a recording medium 204, a reproducing circuit 205, a demodulator 206, and an ECC decoder 207.
In the case of recording data on the recording medium 204, first, recording data 210 that are to be recorded on the recording medium 204 are supplied to the ECC encoder 201. At the ECC encoder 201, data may be encoded and divided into data blocks in the manner described above. Then, the data divided into data blocks are transmitted to the modulator 202.
At the modulator 202, the divided data are modulated into a modulation code that is suited for the present recording/reproducing system implementing the recording medium 204. For example, the (1, 7) RLL (run length limited) code or the EFM (eight to fourteen modulation code may be used as the modulation code in a case where the recording medium 204 corresponds to an optical disk. The modulated data obtained at the modulator 202 are then transmitted to the recording circuit 203.
The recording circuit 203 converts the modulated data into a recording signal, and supplies the recording signal to a recording head so that the modulated data may be recorded on the recording medium.
In the case of reproducing data from the recording medium 204, a reproducing signal that is detected from the recording medium 204 by a reproducing head is reproduced by the reproducing circuit 205. The reproducing signal is then transmitted to the demodulator circuit 206.
The demodulator circuit 206 demodulates the modulated code data that are modulated in the manner described above to reproduce the data blocks. The reproduced data blocks are then transmitted to the ECC decoder 207.
The ECC decoder 207 accumulates the divided data blocks to generate an ECC sector, and then corrects error data within the generated ECC sector to output decoded data 220.
Generally, recording media such as the optical disk, the magneto-optical disk, the magnetic disk, and the magnetic tape have partial defects that are created during their manufacture. Additionally, defective portions of commutative media such as optical disks and magnetic tape may increase owing to influences from dust and scratches created by mishandling of the media. As is described above, the ECC is provided in order to correct such errors occurring in the reproduced signal.
However, as technology develops for increasing the recording density of a recording medium, a dust particle or a scratch of the same size in such an advanced system may affect a larger amount of data compared to the conventional system. Thereby, dust particles and scratches of the same size in the advanced system may result in the generation of a greater number of data errors compared to the conventional system.
Data decoding using the iterative decoding scheme, which is presently gaining much attention, is an effective method for accurately decoding data in a case where the SNR (signal to noise ratio) of the signal decreases. However, in the case of decoding a reproduced signal including an error that may occur upon its reproduction due to defects in the recording medium (e.g., burst error signal), the likelihood information represented by such a burst error signal may be significantly different from the likelihood information that may be represented by the correct data. In such case, influences from the differing likelihood information may be propagated to the other correctly reproduced data through prior information obtained from a previous decoding result that is used in the data decoding. In this way, error propagation may occur, and desired effects of the iterative decoding may not be sufficiently obtained.
The above described problem may be solved by handling a data block containing the burst error as lost data in the iterative decoding process and conducting an error correction process at the ECC decoder. However, when a burst error resides over two data blocks, these two data blocks need to be handled as lost data. In such case, error correction required for the lost data may be beyond the error correction capacity of the ECC so that the required error correction may not be realized.